Yamaha MX-10000 VU meter fault

Discussion in 'Yamaha' started by hifihouse, Mar 7, 2017.

  1. hifihouse

    hifihouse New Member

    Messages:
    3
    Hi all,
    I have recently ordered the MX 10000 from Japan. The amp works well, but there is a fault on the VU meter of the left channel. The symtoms of the fault are not very clear. Here are some symtoms I observe over a week of testing:
    1) Turn on and play, there is sound output on both channel and the left VU moves as the right one does.
    2) Turn on and play, there is sound output on both channel but the left VU doesn't move. After 10 mins to 2 hours of playing, the left VU starts to move.

    I have no idea what may go wrong with the left VU. Can you please help me to solve the problem?

    Many thanks,
    Andy
     
  2. avionic

    avionic " Black Knights" Subscriber

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    Best SWAG is a poor solder connection in the meters circuitry.Or maybe loose connector/connection.
     
    Uncle Paul likes this.
  3. avionic

    avionic " Black Knights" Subscriber

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    BTW Welcome to AK..
     
  4. SoCal Sam

    SoCal Sam Lunatic Member

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    Don't know if the VU meter has an adjustment pot. If it does, there is a chance the pot has oxidized. Simple cleaning may solve issue.

    MX-10000! Multi-voltage equipped? Or you must have a massive step up transformer. Congrats.
     
  5. hifihouse

    hifihouse New Member

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    3
    The VU is adjusted by the trimpot. Which chemical do you remcommend to clean the oxidized pot?
    I don't know if the input AC of the MX-10000 can be adjusted. I have a look at the cables connecting the mains to the transformer and don't see any switches to change the input AC. I'm using step down transformer.
     
  6. SoCal Sam

    SoCal Sam Lunatic Member

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    Standard residue free contact cleaner will do.
     
  7. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    AC Voltage is on the back of the unit

    If it is a Japanese model only , AC Voltage is 100V not 110V
     
  8. SoCal Sam

    SoCal Sam Lunatic Member

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    And, what happened with the VU meter?
     
  9. hifihouse

    hifihouse New Member

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    3
    I managed to open the amp up and did some test. The trimpots controlling the VU are mounted on the relay board of the amp. Luckily, I own 2 MX-10000. I swapped the relay board of the working amp to the faulty one. It works perfectly. This confirms that there is no bad solder joint in the VU itself.

    I follow Sam's advice on cleaning the trimpot. I don't have access to a good contact cleaning solution. I used the Selleys RP7 spray to clean the trimpot. This cleaning solution works but the result is not clear after a couple of days. I turned on the amp to check after applying the solution. The VU problem remained unsolved. I notice the improvement some days later. The left VU starts to move in about less than 1 minutes since I feed input signal to the amp (much quicker compare to 10 mins or 2 hours before cleaning). I'm testing the amp 3 times today. The problem seem to be solved. The left VU works flawlessly now. I will be giving the amp more test in the next couple of days to confirm if the problem is sorted completely.

    Many thanks for your kind inputs - especially Sam!
     
    Ds2000 likes this.
  10. Uncle Paul

    Uncle Paul AK Subscriber Subscriber

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    I would resolder all the pads on the board you swapped out. My money is on a bad solder connection. I have repaired boards this way that looked perfect - you couldn't spot the bad joint but it was there.
     
  11. Mr. Yamaha

    Mr. Yamaha With Kenwood Subscriber

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